1. Field of the Invention
This invention concerns the field of reaction injection molded elastomers containing internal mold release agents.
2. Description of the Prior Art
Reaction injection molded elastomers such as polyurethanes are becoming quite popular as automobile body parts and other applications. These materials must be molded into the desired shape and demolded quickly to be economical. Heretofore, external mold release agents were applied to the inside of the mold before the injection of the reactive streams which would form the RIM part. A new product called Dow-Corning.RTM. Q2-7119 Fluid, which is a dimethyl siloxane with organic acid groups, has been developed for use in polyurethane RIM elastomers to avoid the necessity of an external application of mold release agent. However, since in polyurethane systems a tin catalyst is required for proper reactivity of the system and since the Dow-Corning product mentioned above is reactive with and not compatible with tin catalysts or isocyanates, a third stream was necessary for the use of the internal mold release agent or the tin catalyst concentration was required to be adjusted. Product bulletins concerning the Dow-Corning internal mold release agent advise that premixing the internal mold release agent with the polyol would result in some gellation of the premix.
Most commercial RIM machines are of the two stream variety, thus limiting the application of the Dow-Corning product.
We have discovered a method whereby the internal mold release agent described above may be used in a two-stream system to make a RIM elastomer of superior properties.